Ovalization of a plastic bottle cap, particularly caps for five-gallon water bottles and the like, is a problem typically caused by packing of too many caps for a particular package design. The caps press down on caps below and cause a slight ovalization of the skirt. Equipment used to mount the cap onto the neck of a water bottle after the bottle is filled with water has difficulty doing so when the skirt of the cap becomes ovalized and, thus, does not match the round shape of the bottle neck.
Some currently used bottle caps are designed with constant thickness skirt dimensions, which provides added rigidity to the skirt and relies primarily on hoop stress to prevent ovalization, but also adds to the weight of the skirt. A large quantity of such caps packed together creates enough added weight to overcome the rigidity of thicker skirts and cause ovalization.
U.S. Pat. No. 5,687,865 of Adams et al. discloses a spill-reduction cap for fluid containers, which cap has a downwardly depending skirt with an interior bead at the bottom edge of the skirt for engaging a bottle neck to prevent dirt from entering under the skirt. One disadvantage of an interior bead is that it results in an undesirable undercut increasing the difficulty of ejecting the cap during a mold ejection process. While the internal bead does add mass to the skirt and may have a de-ovalization effect, the cap of the present invention achieves several advantages over the cap of Adams et al. that are discussed herein.